Pressure is mounting on Prime Minister John Key to sack John Banks over his campaign donations.

Fresh revelations from police files this week have led to further questions about how much Mr Banks knew of $65,000 in "anonymous" gifts from internet mogul Kim Dotcom and SkyCity casino.

In May, Mr Key pledged to fire the small business minister if he had lied over the donations to his failed 2010 campaign to be Auckland super-city mayor.

Yesterday he insisted: "Nothing has changed. He hasn't broken the law ... there is no charge against him."

But Labour's deputy leader, Grant Robertson, said the files, which include sworn statements from Dotcom, his bodyguard and his lawyer, showed Mr Banks had not upheld standards expected of a government minister.

The documents say that Mr Banks told Dotcom's lawyer in February that he could not help Dotcom get medical attention in prison, because “that may backfire on Kim if it became known about the election support". Dotcom is facing extradition to the US on anti-piracy charges.

Mr Robertson told Parliament this was "a clear admission that he did know about the donation from Kim Dotcom, and could remember it as recently as this year".

In a sworn statement, Dotcom also said Mr Banks told him: “I want to help you Kim and I can help you more effectively if no-one knows about this donation.”

Mr Robertson said later: "John Banks lied . . . and by the prime minister's own rules, he should be sacked."

Green Party co-leader Russel Norman said "it seems to be unacceptable behaviour for a minister of the Crown".

"The prime minister should show some backbone and sack John Banks."

Mr Banks' ACT party has a confidence and supply agreement with National.

Police closed their investigation in July, saying electoral laws were broken, but insufficient evidence existed to prosecute. A $15,000 donation from SkyCity and two $25,000 cheques from the German millionaire were all registered as anonymous.

Dotcom says he solicited the donations, and Mr Banks accepted a cheque at a meeting at the casino - but it was a volunteer who declared them anonymous, putting Mr Banks in the clear.

Charges were not pursued over a gift of radio advertising because of a time bar.

Mr Banks did not show up to Parliament's Question Time yesterday. He said he had said everything that "needs to be said".

"There has been an expensive police investigation, no charges, all over, all finished and we move on."